1. Field of the Invention
The present invention relates generally to an apparatus for controlling operation of a four-cycle internal combustion engine (hereinafter also referred to simply as the engine) having an odd number of cylinders by controlling fuel injections, ignition timings and the like for the individual cylinders of the engine on the basis of a reference position signal and a cylinder identification signal. More particularly, the invention is concerned with an engine control apparatus in which the reference positions for the individual cylinders can be determined with an enhanced accuracy and which can ensure a high reliability for the engine operation control.
2. Description of the Related Art
In general, in the four-cycle engine for an automobile or motor vehicle in which four strokes of suction, compression, explosive combustion and exhaust of air-fuel gas mixture are effected, it is required to control optimally the fuel injection and the ignition timing in conformance with the operation state of the engine or motor vehicle. To this end, there is provided a signal generating means inclusive of a sensor in association with a rotatable shaft of the engine for making available a reference position signal indicating reference positions for the individual engine cylinders and a cylinder identification signal for identifying the individual cylinders, respectively. Further, a microcomputer is used for detecting a reference crank angle position for each cylinder on the basis of the signals mentioned above and effectuating timer-based control operation on the basis of the reference positions for the cylinders by determining through calculation the control timing such as the ignition timing, fuel injection timing and/or the like.
FIG. 5 is a block diagram showing an engine control apparatus known heretofore for a four-cycle engine which includes, for example, five cylinders.
Referring to the figure, this known engine control apparatus includes a reference position signal generating means 1 for generating a reference position signal T corresponding to a reference crank angle position on a cylinder basis in synchronism with rotation of an engine (not shown) and a cylinder identification (ID) signal generating means 2 for generating a cylinder identification signal C for identifying a particular cylinder in synchronism with rotation of the engine. Each of the reference position signal generating means 1 and the cylinder identification signal generating means 2 is constituted by a rotatable slit disk mounted, for example, on a crank shaft or a cam shaft interlocked thereto and photo-detectors disposed in opposition to the rotatable slit disk, as described hereinafter.
The reference position signal T and the cylinder identification signal C are inputted to a control means 3 which can be implemented by using a microcomputer and which is adapted to detect the reference positions of the individual cylinders on the basis of the reference position signal T and the cylinder identification signal C and calculate the ignition timing or the like control parameters in dependence on the operation state of the engine to thereby output a control signal (e.g., ignition coil turn-on/off control signal) for controlling, for example, the ignition timing.
As can be seen from FIG. 5, the control means 3 includes a cylinder discrimination unit 31 for generating a cylinder discrimination signal F on the basis of the reference position signal T and the cylinder identification signal C and a timing control unit 32 for generating a control signal (e.g., ignition timing control signal) for each cylinder on the basis of the reference position signal T, the cylinder discrimination signal F and the engine operation state.
FIG. 6 is a perspective view showing typical structures of the reference position signal generating means 1 and the cylinder identification signal generating means 2. Referring to the figure, a slit disk 11 is mounted on a cam shaft 10 which is rotated in synchronism with the rotation of the engine. The cam shaft 10 is adapted to rotate once during a period in which a crank shaft (not, shown) rotates twice. A plurality of slits 12 and 13 are formed coaxially in the signal disk 11 in the direction in which the disk 11 is rotated, wherein the radially outer slits 12 (five arcuate slits corresponding to five cylinders, respectively) are so formed as to generate the reference position signal T for the individual cylinders, while the radially inner slit 13 is adapted to generate the cylinder identification signal C for identifying the particular cylinder.
A pair of light emitter elements 15 and 17 are disposed in opposition to a pair of light receiving elements 16 and 18, respectively, wherein a peripheral portion of the disk 11 having the slits 12 and 13 formed therein is interposed between the light emitter elements 15; 17 and the light receiving elements 16; 18. Thus, the light emitting element 15 and the light receiving element 16 cooperate to constitute a photo-detector disposed in opposition to the trace of the slits 12 for generation of the reference position signal T, while the light emitting element 17 and the light receiving element 18 constitute a photo-detector disposed in opposition to the path of the slit 13 for generation of the cylinder identification signal C.
FIG. 7 is a timing chart which illustrates the reference position signal T and the cylinder identification signal C. As can be seen in this figure, the reference position signal T includes pulses each having a leading edge rising up at a crank angle of B65.degree. (indicating a crank angle 65.degree. before the top dead center or TDC) of each cylinder and a trailing edge falling at a crank angle of B5.degree., wherein the position corresponding to the crank angle of B65.degree. serves as the reference position for a maximum lag with the position corresponding to the crank angle of B5.degree. being termed the second reference position. In terms of the crank angle, the total period of the reference position signal T for the five cylinders amounts to 720.degree., wherein one pulse period for each of the cylinders corresponds to 144.degree.. Further, the pulse width or duration extending from the reference position B65.degree. to tile second reference position B5.degree. corresponds to 60.degree. in terms of the crank angle, and a pulse quiescent duration intervening the second reference position B5.degree. for a given one cylinder and the reference position B65.degree. for the cylinder succeeding to that given one cylinder is 84.degree. in terms of the crank angle.
On the other hand, the cylinder identification signal C contains a pulse of a different waveform for a particular cylinder (cylinder #1 in the case of the illustrated example) which differs in phase from the pulses contained in the reference signal position signal T so that the signal C has different signal levels at the reference position B65.degree. and the initial reference position B5.degree. for the cylinders. By way of example, by imparting such waveform to the pulse of the cylinder identification signal C that it assumes a signal level "1s" at both the crank angle positions B65.degree. and B5.degree., respectively, it is possible to identify discriminatively the particular cylinder from the others. Generation of the pulses of the waveforms mentioned above can be realized by appropriately sizing the slits 12 and 13.
Next, description will turn to operation of the known engine control apparatus shown in FIG. 6 by reference to FIGS. 7 and 8.
When the engine rotates, the reference position signal generating means 1 constituted by the combination of the photoelements 15 and 16 and the slits 12 as well as the cylinder identification signal generating means 2 constituted by the combination of the photo-elements 17 and 18 and the slit 13 generate the reference position signal T and the cylinder identification signal C which have waveforms such as illustrated in FIG. 7, respectively. These signals T and C are supplied to the cylinder discrimination unit 31 and the timing control unit 32 incorporated in the control means 3.
On the basis of the reference position signal T and the cylinder identification signal C, the cylinder discrimination unit 31 discriminates or identifies discriminatively the individual cylinders, while the timing control unit 32 detects the reference positions for the individual cylinders to thereby determine through calculation the control quantity for controlling the ignition timing in dependence on the engine operation state, as a result of which the control signals for controlling the ignition timings for the individual cylinders are outputted from the control means 33. In that case, when the ignition timing is to advance, the timing control (or timer control) is performed with reference to the first reference position B65.degree., while when the ignition timing is to lag, the timing control is then performed with reference to the second reference position B5.degree..
At this junction, it is noted that the reference position generating means 1 is mounted on the cam shaft 10 together with the cylinder identification signal generating means 2, as shown in FIG. 6, wherein the cam shaft 10 is mechanically interlocked to the crank shaft. Consequently, the signals indicating the reference positions B65.degree. and B5.degree. on the cam shaft 10 unavoidably contain error which is ascribable to error in transmission of a driving power from the crank shaft to the cam shaft. For this reason, it is practically impossible or at least very difficult for the timing control unit 32 to control the engine operation on the basis of the reference position signal which lacks a sufficiently high accuracy.
Further, it should be mentioned that detection of the reference position signal T with a high accuracy is required not only for the ignition timing control but also for detection of fluctuation in the engine rotation speed (rpm) on the basis of ratios of the periods between the reference positions as well as detection of occurrence of misfiring in the engine on the basis of change in the engine rotation speed.
As will be appreciated from the above description, the engine control apparatus known heretofore suffers from a problem that because the reference position generating means 1 is mounted on the cam shaft 10 in case the engine includes an odd number of cylinders, the reference position signal T unavoidably contains error components due to the transmission error mentioned above, resulting in that a phase deviation or shift takes place in the reference positions for the control, rendering it practically impossible or very difficult to realize the control with a high or satisfactory accuracy.